Callan’s books were designed to give students of Ontario schools a comprehensive study of the Ontario curriculum. There are course books for all science and math subjects from Gr. 9-12. They were contributed to over several years and include detailed explanations on all topics in math/science education, with an emphasis on common areas where students tend to struggle understanding. They include original diagrams that clearly illustrate concepts that are regularly tested on.  Textbooks contain way too much information which is unnecessary and impractical for a student to learn. Callan's books only contain information that is needed in the curriculum. Also, textbooks only give answers (like 13, or -4 N, etc.) at the back of the book. Callan's books cover the entire course and give full step-by-step solutions to all (more than 300!) problems. Callan's books contain a mix of commonly asked questions in high school and more challenging questions.   The books also include a lot of questions – some over 300 and some over 400 problems solved with full, step-by-step solutions given after each worksheet, quiz, test, unit review and exam. Each question also has the category (KU, COMM, APP, TI) and number of marks that would be attributed to it – so the evaluations are a tremendous tool to practice with.